I think you and the parent are agreeing. :) They didn't know what to make of Feynman's analysis, because it used techniques they weren't familiar with. It was clearly an approximation; were the error terms really ignorable?
They only used 5 when it turned out they couldn't manufacture 7 and had no other choice. So they only trusted his analysis out of desperation / wishful thinking, not out of objective reasoning.
But parent comment is using this as an example to complain about experts from different fields wasting people's time or whatever. But this is a terrible example to use. Feynman brought new insights that never would have occurred to computer scientists. And of course they were cautious at first. But they ended up trusting it enough to go through with manufacturing it. And he was right in the end.
Additionally parent comment complains about people like Feynman not being able to communicate. But there is nothing about that in the story. It goes on and on about how Feynman was a great communicator and explained his ideas clearly.
They only used 5 when it turned out they couldn't manufacture 7 and had no other choice. So they only trusted his analysis out of desperation / wishful thinking, not out of objective reasoning.